Natural Hydrogen Exploration
Natural or “white” hydrogen is increasingly recognized as a promising clean energy source. During the exploration phase, identifying surface and near-surface anomalies indicative of subsurface hydrogen accumulations is critical. Gamma-ray spectrometry (GRS) is emerging as a survey tool in this domain.
Hydrogen Formation and Migration
Natural hydrogen can be generated through several subsurface processes:
Serpentinization: Water-rock reactions involving ultramafic rocks, particularly olivine, generate hydrogen via oxidation of Fe²⁺ to Fe³⁺, forming magnetite and H₂. This is the most prolific and efficient hydrogen source process under geological conditions.
Radiolysis: Breakdown of water by natural radioactivity involving U, Th, and K-bearing minerals in the crust also releases hydrogen.
Once formed, hydrogen can migrate along faults and fractures, often from crystalline basement rocks into overlying sedimentary basins. It may be transported in aqueous solution or as a free gas, and can be trapped by a cap-rock similarly to hydrocarbon systems.
Surface Expression of Hydrogen Seeps
Gamma-ray spectrometry is a geophysical survey tool that is often used to measure alterations in surface geology. Anomalies known as “fairy circles” or “hydrogen seep structures” are found to be key surface exploration indicators.
Fairy circles are circular topographic depressions with inhibited vegetation growth, often linked to gas seepage (hydrogen, methane, helium). These features are observed globally, and the locations with underdeveloped plant growth are often associated with geophysical and geochemical anomalies such as concentrations of radionuclides.
Application of Gamma-Ray Spectrometry in Hydrogen Exploration
GRS detects natural gamma radiation from potassium (40K), uranium (238U), and thorium (232Th) isotopes in the uppermost soil and rock layers. In hydrogen exploration, it plays a complementary role:
Mapping Surface Anomalies: Radiometric anomalies (e.g., low K/Th ratios) have been spatially correlated with fairy circles and suspected seep zones in Australia and USA. Combined with other remote sensing techniques, these anomalies can help to improve the geological understanding of the fairy circles.
Supporting Structural Interpretation: GRS data, often integrated with other surface geophysical methods and magnetrometry, helps delineate faults and crustal boundaries that serve as potential migration pathways for hydrogen.
Notably, in Western Australia, areas of elevated hydrogen soil gas concentrations coincided with distinct radiometric patterns and low K/Th ratios, further supporting the use of GRS in targeting hydrogen seeps.
Summary
While hydrogen systems are still being systematically understood, GRS has demonstrated potential in the early exploration phase. By mapping subtle radiogenic and geochemical anomalies at the surface, GRS provides a non-invasive method to prioritize targets for soil gas sampling and follow-up geophysical surveys.
References
Frery, E., Langhi, L., Maison, M., & Moretti, I. (2021). Natural hydrogen seeps identified in the North Perth Basin, Western Australia. International Journal of Hydrogen Energy. DOI
Jackson, O. et al. (2024). Natural hydrogen: sources, systems and exploration plays. Geoenergy. DOI
Mosquera-Rivera, J. et al. (2024). Preliminary remote spatial analysis of fairy circles: an approximation of hyperspectral and geophysical data from hydrogen seeps. First Break, Volume 42. DOI